The present invention relates to a motor drive control technique and, particularly, to a technique that is effective for control of revolution of a multi-phase brushless motor for use in a hard disk drive (HDD) or the like.
A spindle motor is widely used to drive a magnetic disk in a hard disk system or the like. The spindle motor comprises a brushless DC multi-phase motor and the spindle motor is driven by, for example, an IC dedicated to driving the motor (motor drive IC) and spins the magnetic disk at a high speed.
As a method for driving the spindle motor by this type of motor drive IC, a soft switching method is widely known in which PWM (Pulse Width Modulation) is performed for two phases during current-conducting phase switching to suppress a steep change in current.
In order to spin the spindle motor, it is essential to detect the position of the motor. As a sensor-less method, a technique is known that detects the back electromotive force (BEMF) of the motor during a non-conducting period following the above current-conducting phase switching.
The motor drive IC that performs such soft switching control includes an output section which is comprised of, for example, a plurality of power MOS (Metal Oxide Semiconductor) transistors and a predriver and drives a spindle motor, a DC current detecting section which detects a motor drive current, a BEMF detecting section which detects the back electromotive force of the spindle motor, an A/D (Analog/Digital) converter which converts a voltage appearing in a DC current or a non-conducting phase out of three phases into a digital value, and a logic section.
The logic section includes a PLL (Phase Locked Loop) control loop, a current control loop, a soft switching controller which suppresses a steep change in current, a serial port which receives a command from an MPU (Micro Processing Unit), resisters, and others.
For this type of soft switching control, for example, a method that controls the switching time and dead time according to the characteristics of the power MOS transistors is known (refer to Patent Document 1).
[Patent Document 1]
    Japanese Unexamined Patent Publication No. 2005-278386